Is a dependent variable the result of an experiment?

This decision is up to the experimenter.

For example if you wished to explore whether folk grew taller as they grew older, then you'd plot the height of your subjects against their height.

The Age is the controlling variable, and their Height is the dependent variable. From this you'd get a plot of Age (horizontal axis) against height (vertical axis).

Dependent doesn't mean it depends upon the nature of the variable; rather its plot depends upon the results of the experiment. And by convention is plotted on the vertical (Y) axis.